1. Field of the Invention
The present invention relates to a hydrodynamic machine, especially a hydrodynamic retarder.
2. Description of the Related Art
In the case of hydrodynamic machines, and especially retarders, it is known in the art to take measures in order to reduce the no-load losses. No-load losses shall be understood to be losses which originate in the non-operating state of the hydrodynamic machine in such a way that, unintentionally, a residual torque is transmitted from the primary wheel of the hydrodynamic machine to the secondary wheel of the hydrodynamic machine, and in a retarder from the rotor to the stator, which brakes a respective connected drive apparatus in an undesirable way. This leads to increased fuel consumption in motor vehicles.
Known measures may be, for example, to axially move apart the two blade wheels, which are rotor and stator in the retarder, in the non-operating state in order to thus disturb or prevent a circulatory flow of the residual working medium in the working chamber. Other measures provide for introducing disturbing elements in the working chamber which have the same purpose. Finally, efforts have been made to suck the working chamber empty in the non-operating state, which is the non-braking state in retarders, in order to produce a negative pressure. External pumps, rotary pumps, or reciprocating piston pumps, or suction cylinders have been used for this purpose.
Although the known measures could already contribute to a reduction of the no-load losses, there is still room for improvement. It is especially undesirable that additional energy such as electrical power, is consumed by additional measures or that the constructional efforts for these measures are high.
Reference is hereby made to the following documents concerning the documented state of the art:    DE 512 452 A    DE 26 14 476 A1    DE 677 160 A    DE 102 42 736 A1    DE 299 03 829 U1
What is needed in the art is a hydrodynamic machine in which the losses in non-operating state can be minimized, by a simple constructional configuration and a low energy consumption.